When you have selected "Open With.." when you right click and file, Windows will save the list of programs that you have used. If you want to remove some or all from this list try this out.
Navigate to the key below and expand the extension key that you wish to modify, .txt for example.
Next click on the key named "OpenWithList" and simply delete the letter of the programs that you do not want listed, notepad.exe, winword.exe, etc.
Key:[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\XXX\OpenWithList]
Value Name: a, b, c...
Data Type: REG_SZ
Data:(executable name)
